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Artificial noses have the scent of promise

Could help detect cancer and toxins

By Carolyn Y. Johnson
Globe Staff / September 23, 2009

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For two decades, scientists have strived to build an artificial nose that can mimic what is sometimes called our most elusive sense. Now, with a growing slate of potential applications - detecting cancer in a breath, say, or identifying airborne toxins on the battlefield - the technology is advancing and efforts are proliferating.

In North Grafton, a small startup company, CogniScent, is working on an electronic nose that resembles a yellow Dustbuster and sniffs out everything from molds to dangerous chemicals. At MIT, researchers are working on “RealNose,’’ a Pentagon-funded project inspired by dog noses that aims to use actual biological parts - the smell receptors that recognize odor molecules. And, further afield, the Space Shuttle just returned to earth carrying an “ENose,’’ that spent about six months gathering scent data on the International Space Station.

The work is beginning to pay off, in prototypes of devices that are showing their promise in lab experiments. At CogniScent’s offices, cofounder Joel White recently opened a closed mason jar that held a vial with a beige powder in the bottom. He inhaled, but could not smell the powder - a byproduct of making the explosive TNT. Then, White turned on his company’s gadget. It began to sniff the air, pulling in breaths with a softly whirring fan.

A red light blinked right away, and a readout correctly identified the substance - DNT.

Other researchers are building devices that might one day make finding cancer as simple as taking a breathalyzer test. Last month, scientists reported in the journal Nature Nanotechnology that they used sensors made of tiny gold particles to detect cancer in a breath.

And a small pilot study published this summer found that NASA’s ENose was able to distinguish between two different kinds of cancerous cells.

Despite such encouraging results, the quest for a manmade nose is proving difficult - harder than developing the technology that allows computers to pick up sound waves humans can’t hear, or the cameras that capture images our eyes can’t see.

“The chemical senses - the sense of smell and taste - are not as well understood currently as some of the other senses, like vision and audition,’’ said White.

Detecting sound vibrations or light waves is relatively straightforward compared with figuring out how to sense a particular odor molecule, a task made more difficult by the fact that researchers are trying to distinguish very faint scents - the equivalent of discerning less than one teaspoon of food coloring in an Olympic-size swimming pool.

All the research is revealing just how enigmatic the sense of smell really is. Researchers Linda Buck and Richard Axel won the Nobel Prize in 2004 for discovering genes containing the recipes for smell receptors - proteins that detect specific odor molecules and send signals to the brain, where the smells are identified.

But deciphering exactly how these receptors work is challenging.

That means researchers trying to create an artificial nose work with a much narrower goal than identifying all smells in the environment, from the scent of a stinky diaper, a pot of soup, or a rose. Instead, most noses are being designed for specific tasks, such as recognizing a house with mold growing in it, or finding a hidden landmine.

CogniScent is also developing an electronic nose that can detect and alert first responders to potential hazardous agents, such as phosphine, a toxic gas stored in a tank in the back of the lab. The system depends on optical sensing. Inside the guts of Cogniscent’s nose, lights shine on a cartridge made up of different sensors, each a mixture of dye and a polymer.

When an odor molecule interacts with a specific polymer, it changes the way the light looks, and the device is trained to rec ognize different patterns of electronic signals as different chemicals.

That takes some cues from an actual nose, but is also much simplified, with only 16 sensors.

“Nature has done a remarkable job. . . . Over the eons, it’s developed this ability to sense and distinguish between literally thousands of different chemicals and translate that information into the brain,’’ said Harry Tuller, a professor of ceramics and electronic materials at MIT. “But the human nose can’t be used everywhere, can’t be used continuously, and [for] many applications, you need a much more specific sensitivity to something very dangerous a nose can’t pick up.’’

Tuller uses coatings on resonating structures that interact chemically with odor molecules in ways that can be measured, technology being developed by a startup company, Boston MicroSystems. The applications include detecting explosives, chemical warfare agents, toxins, and even breath analysis for medical purposes. He is also working on using inkjet cartridges that print a film sensitive to odor molecules, which creates the potential for mass-produced sensors.

NASA’s ENose, which recently returned to Earth for evaluation, sniffs substances like ammonia, mercury, sulfur dioxide, and alcohols, designed to register when a chemical has hit one-third the maximum allowable level on a spacecraft.

“It’s designed to tell whether particular targeted chemicals suddenly appear - it’s an event monitor for leaks and spills,’’ said Amy Ryan, principal investigator of the electronic nose development program at Nasa’s Jet Propulsion Laboratory.

Meanwhile, MIT researchers are working on a project funded by the Defense Advanced Research Projects Agency, to create a nose by mimicking a dog’s sense of smell and are using the actual proteins that are sensitized by nature to detect different odor molecules. Researchers at the Center for Biomedical Engineering at MIT last year reported the ability to create large numbers of such proteins, an important step toward creating biologically-based sensors.

“We have all these technologies that replicate our senses,’’ said CogniScent’s White. “It would be nice if we could have a full-blown dog nose in a box.’’

Carolyn Y. Johnson can be reached at cjohnson@globe.com.

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